1. Field of the Invention
The present invention relates to a cooling system of ring segment of a gas turbine and to a gas turbine.
2. Description of the Related Art
Conventionally, since combustion gas of a high temperature and high pressure passes through the turbine of a gas turbine, which is used in the generation of electrical energy, cooling of the ring segment and the like is important in order to continue stabilized operation. In particular, due to improvements in the thermal efficiency of gas turbines in recent years, the temperature of combustion gas continues to increase.
FIG. 11 is a cross-sectional view that shows the internal structure relating to the turbine of a gas turbine. The gas turbine supplies combustion gas FG generated in a combustor 3 to turbine vanes 7 and turbine blades 8, and by causing the turbine blades 8 to rotate around a rotating shaft 5, converts rotational energy into electrical power. The turbine vanes 7 and the turbine blades 8 are alternately disposed from the upstream to the downstream of the flow direction of the combustion gas FG. Moreover, a plurality of turbine blades 8 is disposed in the circumferential direction of the rotating shaft 5, and thus rotate together with the rotating shaft 5.
Moreover, the turbine vanes 7 are disposed on the upstream of the turbine blades 8 in the flow direction of the combustion gas FG, and a plurality are disposed in the circumferential direction of the rotating shaft 5, similarly to the turbine blades 8. A ring segment 60 is disposed annularly on the outer periphery side of the turbine blades 8, and between the ring segment 60 and the turbine blades 8, a tip clearance is provided in order to avoid mutual interference.
FIG. 12 is a cross-sectional view of a conventional ring segment. The ring segment 60 is formed from a plurality of segment bodies 61, and is oriented annularly in the circumferential direction of the rotating shaft 5. Each segment body 61 is supported by a casing 67 via hooks 62 of the segment body 61 and an isolation ring 66. Moreover, a collision plate 64 that is supported from the isolation ring 66 is equipped with a plurality of small holes 65. In the segment body 61, a plurality of cooling passages 63 are disposed in the axial direction of the rotating shaft 5.
In order to cool the ring segment 60, cooling air CA which is a portion of bleed air of a compressor is supplied to each segment body 61 of the ring segment 60 from a supply hole 68 of the casing 67. The cooling air CA jets into the space enclosed by the collision plate 64 and the segment body 61, through the small holes 65 opened in the collision plate 64, and carries out impingement cooling of the outer circumferential surface of the segment body 61. Furthermore, when the cooling air CA after the impingement cooling jets into the combustion gas space from the downstream end of the segment body 61 in the flow direction of the combustion gas (in the direction from the left side to the right side on the sheet of FIG. 11) via the cooling passage 63, convection cooling of the segment body 61 is carried out by the cooling air CA that flows through the cooling passage 63.
Japanese Unexamined Patent Document No. H11-22411 (hereinafter, Patent Document 1) discloses a ring segment that is provided with the abovementioned collision plate. An example is illustrated in which when the cooling air that that has performed impingement cooling is supplied to opening portions that are disposed in the outer circumferential surface of the ring segment (segment body) and discharged from the downstream end of the ring segment in the flow direction of the combustion gas FG to the combustion gas space via the cooling passage (cooling air holes), it cools the ring segment.
Japanese Unexamined Patent Document No. 2004-100682 (hereinafter, Patent Document 2) discloses a structure that is an improvement on that disclosed in Patent Document 1. A cooling passage (first passage) that jets a portion of cooling air that has performed impingement cooling from the upstream end of the ring segment (segment body) in the flow direction of the combustion gas to the combustion gas space is disclosed, and a cooling passage (second passage) that jets a greater part of the remaining cooling air after the impingement cooling from the downstream end in the flow direction of the combustion gas to the combustion gas space is disclosed. Thereby, cooling of the ring segment is enhanced.
However, in the invention disclosed in Patent Document 1, there is a region in which a cooling passage is not disposed on the upstream end portion of the ring segment in the flow direction of the combustion gas, and so in the case of the combustion gas further increasing in temperature, the problem arises of the upstream end portion of the ring segment being damaged thermally by the high temperature combustion gas.
Also, in the invention disclosed in Patent Document 2, when a portion of the cooling air after the impingement cooling is discharged from the upstream end portion of the ring segment in the flow direction of the combustion gas to the combustion gas space via the cooling passage (cooling air holes), it enhances the cooling of the upstream end portion of the ring segment. However, since the cooling air that is discharged to the upstream end side of the ring segment in the flow direction of the combustion gas is discharged to the combustion gas space cooling only the upstream end portion, the problem arises of it becoming a loss of the amount of cooling air, and an increase in the amount of cooling air leads to a reduction in the thermal efficiency of the gas turbine.
The present invention was achieved in view of the above problems, and has as its object to provide a cooling system of a ring segment that has as its object to prevent thermal damage of the ring segment as the combustion gas increases in temperature and improve the thermal efficiency by reducing the amount of cooling air, and a gas turbine.